1. Field of the Invention
The present invention relates to a water-jet propulsion personal watercraft and, more particularly to a personal watercraft equipped with a supercharger configured to supply air taken in from outside to an engine mounted in the personal watercraft.
2. Description of the Related Art
In recent years, water-jet propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. Generally, personal watercraft are configured to accommodate an engine within an inner space of a body formed by joining a hull and a deck covering the hull from above to each other at their peripheries. The engine is configured to drive a water jet pump, which pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. As a result, the personal watercraft is propelled.
The engine is configured to generate a driving force according to the amount of a rider's throttle operation of a throttle lever attached to an upper portion of the deck, thereby gaining a propulsion force to propel the watercraft.
In some personal watercraft, various devices are made to increase the power output of an engine of equal displacement. For example, Japanese Laid-Open Patent Application Publication No. 2001-146197 discloses a personal watercraft equipped with a turbocharger in order to efficiently increase power output from an engine. The turbocharger, which is one type of forced induction system, includes a built-in turbine that rotates under influence of the flow of an exhaust gas, pressurizes air taken in from outside, and supplies the pressurized air to the engine. Since the turbocharger can increase the amount of air supplied to the engine, a higher power is gained in the engine.
The turbocharger can increase a boost pressure of the taken-in air by a faster flow of the exhaust gas for rotating the turbine. Accordingly, personal watercraft equipped with a turbocharger are typically constructed such that the turbocharger is positioned in the vicinity of an exhaust port of the engine to supply the faster flow of the exhaust gas to the turbine. This configuration is exhibited by the the personal watercraft disclosed in the publication No. 2001-146197.
Since the built-in turbine in the turbocharger rotates by the flow of the exhaust gas, an effect peculiar to turbochargers, referred to as “turbo lag,” takes place. Undesirably, turbo lag tends to cause a slow response in the change in rotation of the turbine with respect to change in the engine speed of the engine and therefore, tends to cause delay in change in a propulsion force in response to the rider's throttle operation.
In order to reduce an air-intake resistance in an air-intake pipe through which the turbocharger and an air-intake port of the engine communicate with each other, it would be desirable to shorten the length of the air-intake pipe. However, as described above, the turbocharger is positioned in the vicinity of the exhaust port, and hence relatively distant from the air-intake port. For this reason, the turbocharger and the air-intake port communicate with each other through a relative long air-intake pipe, which makes it difficult to reduce the air-intake resistance in the air-intake pipe.